The site isn't working properly for me either. Trying to register the other half and it just crashed. Now when i go back in it says his user name is registered, but when I try and log in get an error. Hm.
We've done this race a few times, the last time on cross bikes. If you don't have a cross bike I would definitely do what you can to favour the road biking section. Before I had a cross bike I used my mountain bike and found the road sections a grind.
As others have said there is a little bit of single track that you might push on, but I did that anyway as I'm pants at mountain biking. Bigger worry is punctures so whatever you use good tyres are the order of the day.
Very sorry to be missing the race this year. Will be thinking of you all on that descent in to the final kayak (how on earth can you have bogs on that steep a slope?!).